ARM Data Discovery

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Instrument : Doppler Lidar (DL)

General Overview

The Doppler Lidar (DL) is an active remote sensing instrument that provides range- and time-resolved measurements of radial velocity and attenuated backscatter. The principle of operation is similar to radar in that pulses of energy are transmitted into the atmosphere; the energy scattered back to the transceiver is collected and measured as a time-resolved signal. From the time delay between each outgoing transmitted pulse and the backscattered signal, the distance to the scatterer is inferred. The radial or line-of-sight velocity of the scatterers is determined from the Doppler frequency shift of the backscattered radiation. The DL uses a heterodyne detection technique in which the return signal is mixed with a reference laser beam (i.e. local ocsillator) of known frequency. An on-board signal processing computer then determines the Doppler frequency shift from the spectra of the heterodyne signal. The energy content of the Doppler spectra can also be used to determine attenuated backscatter.

The DL operates in the near-IR (1.5 microns) and is sensitive to backscatter from micron-sized aerosols. Aerosols are ubiquitous in the low troposphere and are ideal tracers of atmospheric winds. Thus, in contrast to radar, the DL is capable of measuring wind velocities under clear-sky conditions with very good precision (typically ~10 cm/sec). The DL also has full upper-hemispheric scanning capability, enabling the three-dimensional mapping of turbulent flows in the atmospheric boundary layer. When the scanner is pointed vertically, the DL provides height- and time-resolved measurements of vertical velocity.

Output Value-Added Products

This instrument is an input to the following value-added products, which provide improved measurements or derived quantities.